IBM T.J. Watson Research Center, 1101 Kitchawan Road, Yorktown Heights, NY 10598, USA.
Ultramicroscopy. 2013 Feb;125:72-80. doi: 10.1016/j.ultramic.2012.09.007. Epub 2012 Oct 12.
The Contrast Transfer Function (CTF) describes the manner in which the electron microscope modifies the object exit wave function as a result of objective lens aberrations. For optimum resolution in C₃-corrected microscopes it is well established that a small negative value of C₃, offset by positive values of C₅ and defocus C₁ results in the most optimal instrument resolution, and optimization of the CTF has been the subject of several studies. Here we describe a simple design procedure for the CTF that results in a most even transfer of information below the resolution limit. We address not only the resolution of the instrument, but also the stability of the CTF in the presence of small disturbances in C₁ and C₃. We show that resolution can be traded for stability in a rational and transparent fashion. These topics are discussed quantitatively for both weak-phase and strong-phase (or amplitude) objects. The results apply equally to instruments at high electron energy (TEM) and at very low electron energy (LEEM), as the basic optical properties of the imaging lenses are essentially identical.
对比度传递函数（CTF）描述了电子显微镜由于物镜像差而对物体出射波函数进行修正的方式。对于经过 C₃ 校正的显微镜来说，最佳分辨率已经得到很好的证实，即 C₃ 的小负值，由 C₅ 和聚焦 C₁ 的正值抵消，会产生最理想的仪器分辨率，因此 CTF 的优化一直是多项研究的主题。在这里，我们描述了一种 CTF 的简单设计过程，它可以在分辨率极限以下实现信息的最均匀传递。我们不仅解决了仪器的分辨率问题，还解决了在 C₁ 和 C₃ 存在小干扰时 CTF 的稳定性问题。我们表明，可以以合理和透明的方式在分辨率和稳定性之间进行权衡。这些主题都针对弱相位和强相位（或幅度）物体进行了定量讨论。这些结果同样适用于高电子能量（TEM）和极低电子能量（LEEM）的仪器，因为成像透镜的基本光学性质基本相同。
